NEW STUDY LINKS DIOXIN TO HUMAN CANCER.

A new study published last month provides fresh evidence that
dioxin [TCDD] causes cancer in humans. Dioxin is not a commercial
product but is created as an unwanted byproduct of many
industrial processes; significant quantities of dioxin are
released from the smoke stacks (and the ash landfills) of
incinerators that burn chlorine-containing items--such as medical
wastes (RHWN #179), sewage sludge, and municipal solid wastes.
Once it is released into the environment dioxin persists for a
very long time, enters food chains, and accumulates; when humans
eat dioxin contaminated food, such as milk or fish, the humans
themselves accumulate dioxin in their blood and fatty tissues. [1]

Scientists have known since the mid-1960s that dioxin is an
extremely powerful promoter of cancer in laboratory animals, but
industry researchers have recently been claiming that humans
somehow are exempt from the dioxin danger. The question of
dioxin's hazard to humans took on real urgency in the early '80s
when 15,000 veterans sued Dow chemical and other producers of
Agent Orange (a dioxin-contaminated herbicide widely used to
defoliate the jungle in Vietnam from 1962 to 1971); the vets
sought money damages for health effects (cancer, defective
offspring, and so forth) they said they were experiencing.
Lawyers for the Vietnam vets offered documentary evidence that
Dow chemists convened a private meeting of their competitors in
1965 to share new information that impurities [dioxins] in the
herbicide 2,4,5-T (principal component of Agent Orange) caused
severe liver damage in rabbits. According to court records, a
chemist at Hercules Powder Company who attended the private Dow
meeting in 1965, received a phone call from a Dow executive who
"warned him to keep the findings away from the federal
government," according to a reporter for Nature, the British
science journal. [2] If this is true, it would not be the first
time, nor the last, that money has influenced the outcomes, and
the uses, of scientific studies.

In any case, as a result of these lawsuits, during the 1980s the
question of dioxin's effects on humans became subject of bitter
controversy--with enormous sums of money riding on the outcome of
the debate. As the 1980s drew to a close and it became known that
all incinerators create and release dioxin into the local
environment, industry felt enormous pressure to "prove" that
dioxin was harmless to humans. From 1980 onward, industry
researchers published several studies of dioxin-exposed workers,
claiming to show that they suffered no more cancer than the
general public. Last year, however, evidence began to accumulate
indicating that the industry-funded studies of dioxin dangers to
humans were badly flawed or were simply fraudulent (see RHWN #171, #173, #175).

The latest study is not by industry researchers but by Dr.
Marilyn Fingerhut of the federal National Institute for
Occupational Safety and Health (NIOSH); Fingerhut looked at the
health of 5172 workers at 12 chemical plants that manufacture (or
formerly manufactured) products contaminated with dioxin such as
the herbicides 2,4,5-T, Silvex, Ronnel, Erbon, and
pentachlorophenol (which has also been used as a fungicide,
algicide, and wood preservative for telephone poles and pilings),
and the bacterial cleansing agent, hexachlorophene--until the
1970s, a leading bactericide in hospitals.

Of the 5172 exposed workers (all of whom were male), 1520 met two
key conditions: they had been exposed for at least a year, and
their exposure had begun at least 20 years previously. The onset
of cancer is always delayed by 7 to 40 years (or more) between
the time of initial exposure and the time disease appears;
therefore, the "latency" period of at least 20 years is important
in studying cancer that may be related to a particular chemical
exposure. This group ("cohort," to use the language of medical
researchers) had nine times (900%) the normal amount of soft
tissue sarcoma--malignant cancer of the soft connective tissues.
The same group also had 42% more cancers of the respiratory tract
(trachea, bronchus and lung) than would be expected among males
in the general public; by various means, Dr. Fingerhut examined
and tried to eliminate the possibility that tobacco smoking
explained the increase in respiratory cancers.

Among the entire cohort of 5172 men, the occurrence of all
cancers was significantly increased, by 15%; in the high-exposure
group of 1520 men, the "all cancers combined" increase was even
more pronounced--46%; furthermore "all cancers combined" were
increased among workers at nine of the 12 plants studied. Even
when cancers of the respiratory tract were omitted in an attempt
to eliminate smoking as a possible the cause, "all cancers
combined" was increased among the 5172 and even more so among the
high-exposure 1520.

Dr. Fingerhut says correctly that her results do not prove that
dioxin causes cancer in exposed workers. The workers she studied
were exposed to many other chemicals, in addition to dioxin, on
the job, and these other chemicals could explain the cancer
increases she observed.

Nevertheless, the Fingerhut study makes it ever more difficult
for the purveyors of dioxin-creating machines (such as
incinerators for solid waste, hazardous waste, or sewage sludge)
to claim that their dioxin emissions are negligible or harmless.
Because dioxin accumulates in the food chain, even small amounts
can build up to significant levels as time passes.

An editorial in the NEW ENGLAND JOURNAL OF MEDICINE tried to shed
light on the meaning of the Fingerhut study the day it
appeared. [3] The well-known Canadian biostatistician, John
Bailar, wrote, "This evidence is short of proof, as the authors
explain, but it must be taken seriously as a flag of a probable
human risk. If one accepts the best estimate of excess risk given
here (3 deaths observed among the 1520 workers minus 0.3 expected
deaths equals 2.7), the lifetime risk of death from TCDD-related
soft-tissue sarcoma is already approaching 2 per 1000 workers,
and it may increase with additional follow-up study. This
estimate falls in a range that is widely considered unacceptable
for occupational hazards, and it is far in excess of the usual
limits for lifetime risk to the public of 1 per 100,000 or 1 per
million. "Despite the problems, which Fingerhut et al. carefully
note, this work is a model of its kind. Occupational cohort
studies are inherently difficult and uncertain, and we are likely
to wait a long time for appreciably better or broader evidence of
the effects of TCDD [dioxin] on human health....